A senes of RU2(II,III) complexes containing the bulky carboxylate ligand 2,4,6- triisopropylbenzoate (TiPB) of form trans-[Ru2(TiPB)2(02CCH3)2X] [X = Cl 1, PF6 2] and [Ru2(TiPB)4X] [X = Cl 3, PF6 4] have been synthesised. The corresponding RU2(II,II) complexes trans-[Ru2(TiPB)2(02CCH3)2] 5 and [Ru2(TiPB)4] 6 were also isolated. The Ru-Ru bond length in the RU2(II,II) complex 6 [2.2425(6) A] is the shortest observed for a diruthenium tetracarboxylate and, surprisingly, is 0.014 A shorter than in the analogous RU2(II,III) complex 4, despite an increase in the formal bond order from 2.0 in the RU2(II,II) complex 6 to 2.5 in the RU2(II,III) complex 4. This is rationalised in terms of the extent of internal rotation about the RU2 core. This was supported by DFT calculations on the model complexes [RU2(02CH)4]OI+, that demonstrate the relationship between Ru-Ru bond length and internal rotation. The mixed carboxylate complexes trans-[Ru2(02CCH3)2(02CAr)2Cl] 7 and trans[ RU2(02CCH3)2(02CAr)2] 11 (02CAr 2,6-di(p-tolyl)benzoate) have been synthesised along with [Ru2(02CAr)4(CH2Cb)Cl] 9 and [RU2(02CAr)4] 12 complexes. The structure of 9 is a rare example of a structurally characterised dichloromethane complex. The bulky -02CAr ligand protects the axial positions from intermolecular interactions in the absence of strong nuc1eophiles for 9 and 12, and the effect this has on the electronic structure of the diruthenium core in these complexes was investigated. Complexes [RU2(,l1-0)2CU-TiPB)2(TiPB)2] and [RU2(,l1- OMe )2(,l1-TiPB)2(TiPB)2] were structurally characterised using crystals obtained from decomposition of [Ru2(TiPB)4] solutions. [RU2 TiPB)4] is capable of activating dioxygen, and can act as a biologically-inspired catalyst for the aerobic oxidation of alcohols to aldehydes. The synthesis of the diosmium tetracarboxylates [Os2(TiPB)4Cb] 15 and [Os2(TiPB)2(02CCH3)2Cb] 16 is also reported and the electronic structure of these complexes is probed with the aid of DFT calculations.